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The present invention relates to an apparatus and method of forming and shaping a metal can blank to a geometric configuration most suitable to contain pressurized liquids, such as carbonated beverages. More particularly, the present invention relates to a novel and improved double action bottom former capable of operating at a high cyclic rate for a sustained period of time with appreciable capability to repeatedly form and shape can bottoms of a specified thickness.
It has been conventional in the prior art to form and shape the bottom wall of cans using a bottom former assembly generally comprising an inner die and an outer die circumferentially positioned thereabout. Often the prior art describes the inner die as the dome plug and the outer die as the clamp ring, both of which cooperate with the functioning of the ram generally made part of the bodymaker. As the ram carries a metal can blank for contact with the domer assembly, the clamp ring engages the bottom portion of the metal can blank radially outward from the area to be formed with an inwardly-protruding dome. Subsequently, as the ram fitted with the metal can blank resiliently travels with the clamp ring, the dome plug is engaged to form the desired dome profile of the bottom wall of the can blank. It is generally desirable to set the ram forward of the end of the stroke of the ram to generate overtravel thereof to ensure bottoming out of the ram for complete formation of the inwardly-protruding dome and desired thickness of the bottom wall of a can.
Preferably, the clamp ring and dome plug are resiliently held in a longitudinal working position as the ram travels to and within the bottom former assembly. A number of prior art references teach the resilient positioning of the clamp ring and dome plug through configuration of the bottom former assembly with mechanical springs acting alone or in conjunction with a reservoir having pressurized fluids contained therein. For instance, U.S. Pat. No. 4,790,169 issued to Johansson et al. describes therein the use of springs for both the clamp ring and the dome plug and U.S. Pat. No. 4,930,330 issued to Weishalla, which is presently owned by the Assignee of the present invention, describes therein the use of a fluid actuator for resilient positioning of the clamp ring and a plurality of urethane springs for resilient positioning of the dome plug.
Although Weishalla adequately provides for adjustability of the forces acting on the clamp ring, which provides for greater output capabilities in some instances, there continues to be problems associated with the control of such forces acting thereon to shape and form metal can blanks without substantial failure during high cyclic operation.
The Assignee of the present invention has discovered that in some instances the bottom of the metal can blank has a tendency to split at the periphery thereof as the production rate substantially increases from approximately 300 to 500 containers per minute. This occurrence is mainly attributed to the ability to adequately control the forces acting on the clamp ring as the bottom of the can engages thereto. Generally, the ability to control the forces acting on the clamp ring is limited in part or related to the operating components responsible for resilient positioning of the clamp ring, such as a pressurized medium acting on a movable piston, as seen in Weishalla, or a spring of known physical properties or characteristics, as seen in Johansson et al.
In the attempt to provide a satisfactory solution to the problem, the pressure reservoir or chamber is generally optimized or increased in size to the extent of alleviating the pressure buildup on components generally responsible for resilient positioning of the clamp ring. By allowing for gas expansion, and thus reducing the pressure buildup on the resilient-positioning components, the clamp ring is permitted to adequately engage the bottom of the metal can blank for noticeable reduction in failure rates even during high cyclic operation, while improving the bottom former""s ability to form can bottoms having thinner walls. However, the ability to increase the effective volume of the pressure chamber may be limited or not possible due to the design or configuration of those components comprising the typical bodymaker. In attempt to circumvent these design limitations, the art teaches modification of the bottom former assembly to include a surge tank or canister that is in hydraulic communication with the pressurized reservoir. However, in most instances, pressure buildup will continue to occur given the means in which the surge tank is joined with the pressure reservoir, which often only includes a pipe or a hose having limited capacity to effectively transfer fluid to and from the surge tank and back into the pressurized reservoir within the short cycle time generally allowed in such operations.
The Assignee of the present invention also observed in the art substantial mechanical failure of components generally comprising the bottom former assembly. Mechanical failure of mechanisms responsible for resilient positioning of the clamp ring and dome plug generally arise as the ram is inadvertently overextended during high cyclic rates or is configured to overextend to ensure bottoming out of the ram for complete formation of the inwardly-protruding dome. Generally, the art teaches configuration of the ram to overextend in order to exert an adequate amount of force to form the can bottom of specified wall thickness. As a consequence of an excessive overextension of the ram, the components generally responsible for resilient positioning of the dome plug, as well as other components comprising bodymaking equipment, prematurely wear necessitating immediate replacement as they can no longer meet the close tolerances required for adequate formation of the can bottom. Under other operating environments where the ram is not overextended, the spring responsible for the resilient positioning of the dome plug may not be adequately compressed, resulting in a decreased spring force as the preset compression of the spring is generally fixed by the manufacturer. As this occurs, again the dome plug will fail to adequately form can bottoms of specified thickness during high cyclic operation.
Accordingly, there remains a need for a bottom forming apparatus which can adequately operate at a high cyclic rate for a sustained period of time without substantial deleterious impact on components responsible for resilient positioning of the clamp ring and the dome plug, minimize the time required to access and repair components comprising the bottom former assembly, provide an affordable and inexpensive alternative to replacing components responsible for resilient positioning of the dome plug while retaining the preset compression of the spring, and attain greater capability of allowing the ram to overextend without substantial impact or damage to the components comprising the bottom former and, in general, to other bodymaker components.
In order to overcome the numerous drawbacks apparent in the prior art, an improved device for forming can bottoms of specified thickness has been devised.
It is thus an object of the present invention to provide a bottom former capable of greater control of forces acting on the clamp ring through incorporation of an expanded gas chamber to allow for gas expansion and less pressure buildup on operating components generally responsible for resilient positioning of the clamp ring.
It is another object of the present invention to provide a bottom former that is readily adaptable to fit existing bodymaking equipment without undue difficulty or substantial modification of components generally comprising the bottom former.
It is another object of the present invention to provide a bottom former that is capable of utilizing biasing means comprising a donut spring made from a low durometer material to greatly enhance the control of components generally responsible for resilient positioning of the dome plug during high cyclic operation.
It is another object of the present invention to provide a bottom former having means to restore the pre-load force of the biasing means and increase the life thereof by as much as 15% without resorting to replacement of components generally responsible for resilient positioning of the dome plug.
It is another object of the present invention to provide a bottom former having the capability of operating under less pressure buildup to reduce the force on the clamp ring to permit adequate material flow for elimination of split can bottoms during forming operations.
It is another object of the present invention to provide a bottom former that is capable of accurate production of can bottoms having a thinner wall and an accurate dome-shaped profile.
It is another object of the present invention to provide a bottom former that is less prone to mechanical failure as a result of operating at a high cyclic rate for a sustained period of time.
It is yet another object of the present invention to provide a bottom former that is economical, durable, and fully effective in performing its intended functions.
In accordance with the present invention, an improved double action bottom former substantially capable of forming and shaping a metal can blank at a high cyclic rate, the bottom former comprising an integral cylinder housing member having a first end portion and a second end portion. The first end portion generally comprises an elongate cylinder with sidewalls defining a first axial chamber of a first known diameter. The second end portion generally comprises a cylinder with sidewalls defining a second axial chamber with a second known diameter, which is larger than the first known diameter. The first and second axial chambers are separated by an integral chamber separator. The second axial chamber comprises a cover plate having a large aperture extending therethrough to permit hydraulic communication with a third axial chamber. The first end portion sidewalls of the integral cylinder housing member further comprises a plurality of axially oriented bores extending from the first end portion of the integral cylinder housing member through the integral chamber separator and into the second axial chamber. Push rod means comprises a plurality of pushrods slidably positioned within an equal number of pushrod bushings fitted within an equal number of axially oriented bores present within the first end portion sidewalls of the integral cylinder housing member and integral chamber separator. Each of the pushrods generally comprises a first end and a second end. Biasing means are provided for operatively biasing the cover plate and preferably comprises a donut spring having a cylindrical-shaped aperture extending therethrough to define a third axial chamber. The donut spring, generally made from low durometer materials, comprises exterior and interior recesses for fitting engagement of a plurality of washers and an equal number of standoff tubes having a longitudinal bore extending therethrough for passage of an equal number of tension bolts to fixedly hold the spring end plate and donut spring to the bottom former and set the pre-load force of the donut spring. Tool set means, located at the first end portion of the integral cylinder housing member, comprises a clamp ring and a dome plug for contacting and shaping a metal can blank fitted to a conventional press arm. Preferably, the clamp ring is circumferentially fitted around the dome plug in abutting engagement with the first end of each of the pushrods. Piston means, which resiliently positions the clamp ring and pushrod means, comprises a piston member movably positioned within the second axial chamber. Preferably, the piston member comprises an annular piston wall fixedly attached to the periphery of a concave-shaped bottom having a concave receiving surface. The annular piston wall generally comprises a contact surface facing the integral chamber separator and principally serves as a contact surface for the second end of each of the pushrods. The concave receiving surface provides means to uniformly distribute the acting force on the piston member as a pressured medium enters into and fills the second and third axial chambers via an axially aligned port established at the spring end plate. In terms of operation, as a press arm bearing a metal can blank approaches and contacts the clamp ring, the resultant force is transferred by the pushrod to the contact surface of the piston member, which is generally resiliently positioned by the pressurized medium acting on and against the concave receiving surface of the piston member. Similarly, the resultant force acting on and against the dome plug is axially transferred by the integral cylinder housing member to the biased cover plate and donut spring.